The secret history of nuclear testing and coral reefs


I stumbled cross these stunning satellite images of Bikini and Enewatak Atoll on the Artificial Owl blog. Top left is a 2000m crater left by Castle Bravo in 1954, the second biggest thermonuclear hydrogen bomb (weighing in at 15 megatons, 1200 times more powerful than Hiroshima). Top right is the 120m blast crater in the reef flat created by the Cactus test in 1958. The ‘dome’ construction on the island in the same image is a concrete cover built in 1977 to cover over 85,000 cubic metres of radioactive soil and debris from across the Marshall Islands. I’m staggered by the scale of these tests – whilst I remember the end of the French underground nuclear weapons testing at Muroroa and Fangataufa Atolls in the late 1990’s (after 147 tests had been conducted), I had no idea of the sheer size of the early impact craters left from earlier explosions. The good news is that recent surveys of the coral reefs surrounding Bikini Atoll  shows signs of recovery from the disaster, and the bomb crater itself now supports vibrant and diverse coral communities. However, when  compared to surveys conducted ‘pre-bomb’ in the early 1950’s, at least 28 species of coral have now become locally extinct, most likely as a result of the initial impact, radiation, increased sedimentation or altered atoll hydrology. A few highlight pictures are featured below, but go check out the original postings here and here for more information and photographs.

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Introducing the spookfish – the first known vertebrate to have evolved mirrored eyes

Researchers from Tuebingen University in Germany have made a startling discovery by finding the first known vertebrate to have evolved mirrors, which focus light into the eyes. This odd vertebrate is a species of fish (Dolichopteryx longipes), commonly known as the ‘spookfish‘ or ‘barreleye‘. Although the spookfish has been recognised for over 120 years, it was only recently (last year) that a live specimen was captured of the coast of Tonga.

The reason for their ellusive nature is that spookfish are resident in mesopelagic to bathypelagic zones (~400 to 2,500m depth), inhabiting the border between the photic and aphotic zones. In order to enhance visual acuity at such depths where sunlight barely penetrates, the spookfish has evolved an elaborate system of two sets of connected double eyes. One half of each eye points upwards, capturing the faint light from the surface, whilst the other half point downwards.


The main eyes of spookfish (with the orange-yellow eyeshine from flash photography) are offset with reflective mirrors (indicated here in black) to focus light from above.

These “diverticular” eyes use an elborate mirror constructed of tiny crystals that focus reflected light onto the retina of the eye. Professor Julian Partridge, a co-author on the paper reasons that this system is the reason that the spookfish thrives in such dimly lit regions of the ocean:

“At these depths it is flashes of bioluminescent light from other animals that the spookfish are largely looking for.

The diverticular eyes image these flashes, warning the spookfish of other animals that are active, and otherwise unseen, below its vulnerable belly.

That must give the fish a great advantage in the deep sea, where the ability to spot even the dimmest and briefest of lights can mean the difference between eating and being eaten.”


When viewed from the top of the head, the mirror inside of the diverticulum (marked with an arrow) is clearly visible through the transparent cornea of the eye.

Nature has evolved some absolutely incredible adaptions to environmental conditions – the really neat thing about this study is that it proves that image formation in vertebrate eyes isn’t limited to refraction, a trait that has evolved in nearly every other vertebrate (including mammals).

“In nearly 500 million years of vertebrate evolution, and many thousands of vertebrate species living and dead, this is the only one known to have solved the fundamental optical problem faced by all eyes – how to make an image – using a mirror” (Link)

Click here to read the full paper in Current Biology.

Introducing the giant coconut crab

Believe it or not, this isn’t a photoshopped or altered image – the crab the size of a trash can is the ‘coconut crab‘ (Birgus latro), and can be found throughout the equatorial Indo-Pacific region. These incredible 10 legged creatures grow upto a metre in leg span, with large modified claws that split coconut shells and can lift objects upto 30kg in weight. Although technically the coconut crab can be considered a coral reef associated organism (as it’s larval part of its lifecycle is oceanic) the adults can’t swim and spend their entire lives on land, upto 6km from the ocean (via

National Geographic photographs southern right whales

Amongst the winners of the National Geographic “best wild animal photos of 2008” (link) is this incredible photograph of a diver and a southern right whale, taken in New Zealand. Like most whale populations, the souther right whale was extensively hunted from the mid 18th century up until the early 1970’s, severely depleting the southern Pacific populations around the New Zealand coastal waters . Since the ‘official’ worldwide ban on hunting right whales in 1937, southern right whales began to appear off the coast of New Zealand from the early 1960’s onwards. See the full set of photographs by Brian Skerry over at the National Geographic website (Link)

Rare corals may be smarter than previously thought

Following on from a previous article at Climate Shifts, a recent article published in PLoS One shows that corals are proving to be even more non-conformist than previously thought. Zoe Richards and co-authors from the ARC Centre of Excellence for Coral Reef Studies found that ‘rare’ species of branching corals are able to cross breed with other branching corals to create hybrids, therefore avoiding probable extinction:

“Coral reefs worldwide face a variety of marine and land-based threats and hundreds of corals are now on the red list of threatened species. It is often assumed that rare coral species face higher risks of extinction than common species because they have very small effective population sizes, which implies that they may have limited genetic diversity and high levels of inbreeding and therefore be unable to adapt to changing conditions.

When we studied some particularly rare species of Acropora (staghorn corals), which you might expect to be highly vulnerable to extinction, we found some of them were actually hybrids – in other words they had cross-bred with other Acropora species.  This breaks all the traditional rules about what a species is. By hybridising with other species, these rare corals draw on genetic variation in other species, increasing their own potential to adapt to changing conditions.

When we looked at the genetic history of rare corals, we found that they exhibited unexpected patterns of genetic diversity.  This suggests that, rather than being the dying remnants of once-common species, they may actually be coral pioneers pushing into new environments and developing new traits by virtue of the interbreeding that has enabled them to survive there.

This is good news, to the extent that it suggests that corals may have evolved genetic strategies for survival in unusual niches – and may prove tougher to exterminate than many people feared. With such tricks up their sleeve, it is even possible that the rare corals of today could become the common corals of the future.”  (Link)


“Shipwrecks Wreak Havoc on Coral Reefs”


ScienceNow News, 21st August

Warming seas and ocean acidification aren’t the only hazards facing the world’s coral reefs. A new study suggests that the communities can be thrown quickly and seriously out of balance by the iron from sunken ships. Scientists hope the findings will encourage the prompt removal of derelicts before they can damage the fragile ecosystems.

The problem with shipwrecks appears to be a particularly aggressive reef-dwelling creature called Rhodactis howesii, a type of sea anemone. When nutrients are abundant and there are no predators, R. howesii thrives. Unfortunately, it also eats coral, threatening the foundation of the ecosystem.

Several previous studies have linked shipwrecks and reef degradation, but researchers in Hawaii decided to measure the effect in detail. They surveyed a coral reef off Palmyra, an isolated atoll in the middle of the Pacific Ocean. There they found high densities of R. howesii near a longline fishing boat that sank in 1991. Those densities steadily declined with distance from the wreck; and within about 100 meters, they dropped to zero–with a few exceptions. The exceptions, the team reports today in PLoS ONE, involve navigation buoys installed on the atoll in 2001.

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Rising ocean acidity threatens low-lying islands – Reuters

A woman sits atop a section of a dyke built to protect the tiny island from the ravages of the sea during a sunrise in the Maldives capital Male in this July 12, 2001 file photo.Reuters, 1st June 2008

Rising acidity in the ocean caused by seas absorbing greenhouse carbon dioxide could make low-lying island nations like Kiribati and the Maldives more vulnerable to storms as their coral reefs struggle to survive, say scientists.

Carbon dioxide in the atmosphere is at its highest level in the past 650,000 years, possible 23 million years, and half has now been dissolved into the oceans making them more acidic.

Ocean acidification, which is projected to spread extensively north from the Antarctic by 2100, makes it difficult or impossible for some animals, like coral and starfish, to produce their shells and skeletons.

“If ocean acidification weakens the structure of reef-forming corals and algae, tropical systems (islands) will be more vulnerable to physical impacts from storms and cyclones,” said a new report by some of the world’s leading marine scientists.

“By 2100, it is expected that some reefs will become marginal and reef calcification will decline,” said the report, by the Antarctic Climate & Ecosystems Cooperative Research Centre, released on Monday.

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“Catching corals’ spectacular moment” – BBC News

“By the light of April’s full moon on Sunday or, quite likely a night or two after, corals will be mating en masse. Along the length of the island archipelago that makes up the Republic of Palau, millions of coral colonies will simultaneously release billion upon billion of eggs and sperm into the dark waters.

An hour or so after sunset, each spawning coral will discharge showers of sex cells, packaged in orange and pink blobs. They will rise to the surface in such huge numbers that they may form oily slicks metres long.

If the sea conditions are right, spawn slicks can coalesce to be large enough to be visible from space.

Once on the surface, the packages burst open, liberating eggs and sperm for fertilisation. Countless free-swimming coral larvae then develop and three or four days later, a few will have survived long enough to make it to the sea bed. There they attach to a suitable hard surface and develop into single baby coral polyps. The next generation of corals on the reefs will be launched.

A team of marine biologists from Australia, Britain and the Philippines has come to Palau to take advantage of this wonder of nature in the cause of coral reef restoration.

The scientists are here to investigate the potential of an experimental technique known as coral seeding – in other words, collecting some of the spawn from mass mating events and using it to promote the growth of new corals on reefs in need of rescue.

” (Read more)

Butterfly fish ‘may face extinction’

Wildlife Extra, 29th February 2008

Scientists have warned that a beautiful black, white and yellow butterflyfish, much admired by eco-tourists, divers and aquarium keepers alike, may be at risk of extinction.

The case of the Chevroned Butterflyfish is a stark example of how human pressure on the world’s coral reefs is confronting certain species with ‘blind alleys’ from which they may be unable to escape, says Dr Morgan Pratchett of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.


Highly Specialized Feeding Habit
In a study published in the journal Behavioural Ecology and Sociobiology Dr Pratchett and Dr Michael Berumen of Woods Hole Oceanographic Institution (USA) warn that the highly specialized nature of the feeding habits of this particular butterflyfish – the distinctively patterned Chaetodon trifascialis – make it an extinction risk as the world’s coral reefs continue to degrade due to human over-exploitation, pollution and climate change.

‘The irony is that these butterflyfish are widespread around the world, and you’d have thought their chances of survival were pretty good,’ Dr Pratchett said today. But they only eat one sort of coral – Acropora hyacinthus – and when that runs out, the fish just disappear from the reef.’

Rather Starve Than Change Diet
The team found it hard to believe a fish would starve rather than eat a mixed diet, so they tested C. trifascialis in tank trials on a range of different corals. The fish grew well when its favourite coral was available – but when this was removed and other sorts of corals offered, it grew thin, failed to thrive and some died.

‘We call these kinds of fish obligate specialists. It means they have a very strong dietary preference for one sort of food, and when that is no longer available, they go into decline. We still don’t have a satisfactory scientific explanation for this, as it seems like rather a risky tactic in evolutionary terms – but it must confer some advantage provided enough of its preferred food is available,’ Dr Pratchett says.

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